1. Technical Field
This invention relates generally to internal combustion engines, and more particularly to pistons and their method of construction.
2. Related Art
Engine manufacturers are encountering increasing demands to improve engine efficiencies and performance, including, but not limited to, improving fuel economy, improving fuel combustion, reducing oil consumption, and increasing the exhaust temperature for subsequent use of the heat within the vehicle. In order to achieve these goals, the engine running temperature in the combustion chamber needs to be increased. However, while desirable to increase the temperature within the combustion chamber, it remains necessary to maintain the piston at a workable temperature. As such, it is known to incorporate outer and inner cooling galleries, both open and closed, within the piston head through which engine oil is circulated to reduce the operating temperature of the piston head. The outer cooling galleries typically circulates about an upper land of the piston including a ring groove region while the inner cooling gallery is typically beneath an upper combustion surface of the piston head, commonly referred to as undercrown, which commonly includes a recessed combustion bowl. As such, both the ring belt region and the combustion surface benefit from cooling action of the circulated oil. However, over time the circulated oil begins to degrade and oxidize as a result of contacting the high temperature surfaces, and thus, carbon deposits form on the inner surfaces of the upper land and undercrown. As the carbon build-up continues, an insulation layer is formed on the respective surfaces. As such, the cooling effects of the circulated oil are diminished, which in turn leads to surface oxidation and erosion, as well as over tempering of the upper land and combustion surface regions. As such, the mechanical properties of the piston material are diminished, which can lead to crack formation, particularly at high stressed regions, such as a combustion bowl rim.
A piston constructed in accordance with this invention overcomes the aforementioned disadvantages brought on by the formation of carbon build-up by reducing the tendency for oil deposits to accumulate surfaces contacted by cooling oil. As such, a piston constructed in accordance with this invention realizes enhanced running efficiencies, maintains the strength and durability of the base material throughout use and provides an enhanced useful operating life.